POS0621 EFFECTS OF B CELL DEPLETION BY CD19-TARGETED CAR-T CELLS IN A MURINE MODEL OF SYSTEMIC SCLEROSIS
Authors: J. Avouac, A. Cauvet, C. Orvain, M. Boulch, P. Bousso, Y. Allanore
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Chimeric antigen receptor (CAR)-T cells represent a potentially curative strategy for B cell malignancies. A first successful clinical experience has been reported in systemic lupus erythematosus, suggesting that CD19-targeted CAR-T cell transfer was feasible and tolerable [1]. <h3>Objectives</h3> Since systemic sclerosis (SSc) and SLE are both severe diseases sharing B cell implication in their pathogenesis, we aimed at assessing the efficacy and tolerance of two B cell depletion strategies, including one with CD19-targeted CAR-T cells, in a preclinical model mimicking the severe lung damages observed in SSc. <h3>Methods</h3> B cell depletion strategies were evaluated in the Fra-2 transgenic (Tg) mouse model. We considered a first group of 16 untreated mice, a second group of 15 mice receiving a single intravenous (IV) dose (50 µg) of anti-CD20 monoclonal antibody (mAb) at day 1 and a third group of 8 mice receiving 50 µg anti-CD20 mAb IV at day 1 followed by the IV injection of 20*10<sup>6</sup> CD19-targeted CAR-T cells at day 3. After 6 weeks, different validated markers of inflammation, lung fibrosis and pulmonary vascular remodeling were assessed. <h3>Results</h3> Following treatment with anti-CD20 mAb, CD19 expression was significantly decreased in peripheral blood and lesional lungs of Fra-2 Tg mice by 59% (p&lt;0.001) and 40% (p=0.019), respectively, compared to control Fra-2. B cell depletion was even more pronounced in mice treated with CD19-targeted CAR-T cells: CD19 expression was decreased in peripheral blood and lungs of Fra-2 Tg mice by 92% (p&lt;0.001) and 85% (p&lt;0.001), respectively, compared to control Fra-2. CAR-T cell infusion increased mortality in Fra-2 Tg mice (<b>Figure 1A</b>). In line with the above findings, mice receiving CD19-targeted CAR-T cells displayed a significant increase in lung density (mean difference of 55±28 Hounsfield Units, p=0.038) (<b>Figure 1B-C</b>) and a marked reduction of functional residual capacity (mean difference of 25±9%, p=0.041) as compared to control Fra-2 when assessed by chest micro-CT imaging. CAR-T cell infusion significantly increased lung collagen content (mean difference of 11.93±4.44 µg/mL, p=0.020) (<b>Figure 1D</b>), histological fibrosis score (mean difference 1.74±0.48, p=0.002) (<b>Figure 1E-F</b>) and right ventricular systolic pressure mean difference 8.52±2.70 mmHg, p=0.013) (<b>Figure 1G</b>). CAR-T cells accumulated in lesional lungs and promoted T infiltration and activation: a significant increase of CD4+ effector memory T cells was observed in CD19-targeted CAR-T cell-treated Fra-2 Tg mice compared to Fc control Fra-2 Tg mice (mean difference of 32±%, p=0.001). Moreover, the fraction of CD69 and PD1-expressing cells was significantly increased within the CD4+ and CD8+ subsets in the lung of CD19-targeted CAR-T cell-treated Fra-2 Tg mice. Treatment with anti-CD20 mAb in monotherapy had no impact on lung inflammation-driven fibrosis and pulmonary hypertension. <h3>Conclusion</h3> B-cell therapies failed to show efficacy in the Fra2 transgenic mice. The exacerbated Fra-2 lung inflammatory burden stimulated accumulation and expansion of activated CD19-targeted CAR-T cells, secondarily inducing T-cell activation and systemic inflammation, finally leading to disease worsening. <h3>Reference</h3> [1]Mackensen A et al, Nat Med 2022;28:2124:2132 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.